Elastomeric materials are utilized in numerous industrial applications. For example, elastomeric materials are utilized in the manufacture of tires, hoses, seals, mounting, damping and insulating devices, to name a few. These and other articles have established uses in automotive parts, such as in the engine compartments of automobiles and other vehicles, for example engine mounts, hoses, shrouds, seals, grommets, washers, spacers, covers, and housings, etc. In addition, devices for mounting the engines within these vehicles typically comprise one or more metal parts adhesively bonded to one or more vulcanized elastomeric parts. In these and many other industrial applications utilizing vulcanized or thermoplastic elastomeric materials, the elastomeric materials are typically exposed to degradative elements such as various solvents, oils, fuels and ozone. Elastomeric materials have a tendency to degrade when exposed to these types of materials, and there is a continuing search within industry to provide elastomer articles that are resistant to degradative elements.
One method of rendering elastomeric materials resistant to corrosive materials is to apply a protective coating to the elastomeric material. Various corrosion-resistant coatings previously utilized for both flexible substrates (e.g., elastomeric substrates) and rigid substrates (e.g., steel, stainless steel, aluminum or plastic) include polyurethanes, polysulfides and fluorocarbon elastomers. When applied to rigid substrates, traditional corrosion-resistant coatings such as fluorocarbon elastomers have been found to provide excellent resistance to oil and fuel. However, when applied to flexible elastomeric substrates comprising natural rubber and/or diene-type elastomers and mixtures, the fluorocarbon elastomers suffer from poor fatigue resistance, poor low temperature characteristics, and poor adhesion to these substrates.
U.S. Pat. No 4,774,288 discloses a hydrogenated copolymer of a conjugated diene and an α,β—unsaturated nitrile containing an active phenol-formaldehyde resin vulcanization system. The disclosure is directed to the bulk vulcanizate, which is characterized as having good compression set properties and a good resistance to oils and good resistance to oxidative attack in air at elevated temperature aging under oxidizing conditions, however no mention is made suggesting coatings could be formed on flexible elastomeric substrates such as natural rubber and polybutadiene which might provide useful properties.
U.S. Pat. No. 5,314,741 discloses a coating composition including a latex of highly saturated polymer such as hydrogenated nitrile rubber, highly saturated styrene/butadiene copolymer, hydrogenated polybutadiene, or hydrogenated styrene/vinyl pyridine/butadiene terpolymer. The coating is applied to a substrate and cured in place to yield a desired coated article reportedly resistant to ozone, oxygen, and UV light. Suitable curatives taught are zinc-sulfur cure packages. Elevated temperatures are utilized to affect curing of these coatings. Moreover, conventional vulcanizing systems high in sulfur content and low vulcanization accelerator content, or semi-efficient vulcanizing system having a moderate dosage of sulfur and vulcanizates accelerator known to the expert, and described e.g. in W. Hofmann, Kautschuk-Technologie, Genter Verlag, Stuttgart, 1980 p. 64 and 254–255 have several drawbacks. Conventional vulcanizing systems resulting in vulcanizates with good resistance to dynamic stresses (flex life) are very sensitive to aging and reversion. Semi-efficient vulcanizing systems usually give vulcanizates which have a less of a resistance to dynamic stresses (flex life), but, in return, they are somewhat more stable to aging and reversion (cf. R. N. Datta and W. F. Helt, Rubber World, August 1997, p. 24, et seq.) It has also been observed by the present inventors that coatings based on highly saturated elastomers utilizing vulcanizing chemistry suffer from loss of adhesion to substrates such as blends of natural rubber and diene elastomers widely used in rubber articles in the aforementioned articles, especially tires, hoses and the like. A need exists for an improved protective coating for flexible elastomeric substrates which provide improved adhesion to the surface of elastomers, and improved flex-resistance.
U.S. Pat. No. 5,314,955 discloses a coating composition consisting of (a) a hydrogenated acrylonitrile-butadiene copolymer, (b) a phenolic resin, (c) a curing component, and (d) a solvent. This coating solves many of the problems of adhesion to rubber substrates combined with fatigue resistance and fuel resistance. One of the drawbacks of this coating composition is that it requires a high temperature bake to cure the coating and to promote adhesion to adjacent metal surfaces. A high temperature bake requires heat soaking of the entire article to be coated. Some parts such as helicopter rotor bearings would be damaged by a high temperature bake, therefore coatings such as taught in '955 are not practical to apply. The high temperature bake is also costly in production since it adds a time delay and additional handling of the parts. There still exists a need for improved protective coatings for flexible elastomeric substrates comprising typical natural rubber and/or diene-type elastomers that are resistant to fatigue over a broad temperature range, and that exhibit effective adhesion to the substrate, and that can be cured at room temperature if this is a limiting factor in coating an article.